Infra-red forced air dryer and extractor

Abstract: An infra-red dryer (10) for installation in a printing press (12) utilizes high velocity air jets (98) which scrub and break up the moist air layer which clings to the surface of a freshly printed and/or coated sheet (S). The high velocity air jets are directed through multiple air flow apertures (96) across an array (38) of infra-red lamps (60) onto the freshly printed and/or coated sheets. An extractor (40) exhausts the moisture-laden air from an exposure zone (74) while short wave length infrared radiation heats the ink and/or protective coating. The effective exposure to high velocity, hot air is increased by the air jets which produce a balanced pressure air blanket along the sheet travel path (P). The moist air layer is displaced from the printed and/or coated sheet (S) and is extracted from the press (12) as the sheet moves through the exposure zone (74).

Description: This invention is related generally to accessories for sheet-fed, rotary offset printing presses, and in particular to a dryer for printed materials which utilizes infra-red radiant heat, forced air flow and extraction. In the operation of a rotary offset press, an image is reproduced on a sheet of paper or some other print stock by a plate cylinder which carries the image, a blanket cylinder which has an ink transfer surface for receiving the inked image, and an impression cylinder which presses the paper against the blanket cylinder so that the inked image is transferred to the paper. In some applications, a protective and/or decorative coating is applied to the surface of the freshly printed sheets. The freshly printed sheets are then conveyed to a sheet delivery stacker in which the finally printed sheets are collected and stacked. The wet ink and coatings should be dried before the sheets are stacked or run back through the press for a second pass, to prevent smearing defects and to prevent offsetting of the ink on the unprinted side of the sheets as they are stacked. Spray powder has been applied between the freshly printed sheets which are to be stacked to improve sheet handling and to separate one delivered sheet from the next sheet to prevent offsetting while the ink and/or coating dries. One limitation on the use of spray powder is that fugitive particles of the spray powder disperse into the press room and collect on press equipment, causing electrical and mechanical breakdowns and imposing a potential health hazard for press room personnel. Hot air convection heaters and radiant heaters have been employed to reduce the volume of spray powder applied, except for the small amount needed for sheet handling purposes. Hot air convection heaters are best suited for slow to moderate speed press runs in which the exposure time of each printed sheet to the hot air convection flow is long enough that aqueous base inks and coatings are set before the sheets reach the stacker. For high-speed press operation, for example, at 5,000 sheets per hour or more, the exposure time of each printed sheet as it passes through the dryer station is not sufficient to obtain good drying by convection flow alone. Radiant heaters such as infra-red heat lamps provide greater drying efficiency because the short wave length infra-red energy is preferentially absorbed in the liquid inks and coatings to provide rapid evaporation. The infrared radiant energy releases water and volatiles from the ink and/or coating. Consequently, a humid air layer clings to the printed surface of the sheet as it moves through the dryer, and will be trapped between adjacent sheets in the stack unless it is removed. As press speed is increased, the exposure time (the length of time that printed sheet is exposed to the radiant heat) is reduced. Consequently, it has been necessary to increase the output power of the radiant lamp dryers to deliver more radiant energy to the printed sheets in an effort to compensate for the reduction in exposure time. The higher operating temperatures of the high-powered lamps cause significant heat transfer to the associated printing unit, coater and press frame equipment, accelerated wear of bearings and alterations in the viscosities of the ink and coating, as well as upsetting the water balance of aqueous coatings. The heat build-up may also cause operator discomfort and injury. The operative efficiency of a printing press dryer is improved by a combination of infrared thermal radiation, forced air flow and extraction of moisture and volatiles. US Patent No. 4,809,608 discloses the use of an infrared dryer for a printer in which a pair of rotary fans placed side-by-side direct a drying airflow through respective circular groups of apertures to a series of parallel infra-red lamps. However, such an arrangement produces a non-uniform flow pattern over the surface of a substrate and so has limited efficiency in removing the humid air layer clinging to the substrate. According to the present invention, a dryer is provided for use on a printing press of the type having conveyor apparatus for transferring a freshly processed substrate along a substrate travel path, the dryer including a dryer head adapted for installation in an operative position adjacent said travel path, thereby defining an exposure zone therebetween, the dryer head including a housing defining an air distribution manifold having an inlet port for receiving pressurized air, a reflector plate disposed adjacent the air distribution manifold, the reflector plate being intersected by multiple air flow apertures arranged to direct jets of pressurized air from the air distribution manifold into the exposure zone, and a heat lamp assembly including multiple heat lamps disposed intermediate the reflector plate and the substrate travel path, the multiple air flow apertures being substantially uniformly distributed along the substrate travel path to deliver a substantially uniform blanket of pressurized air across the substrate travel path. Effective exposure to the forced air flow is increased by the multiple air jets produced by the air flow apertures and delivering a substantially uniform blanket of pressurized air across the substrate travel path. Since the release of moisture and other volatiles from the ink and/or coating occurs continuously during exposure in response to the absorption of infrared radiation, the moisture laden air layer is displaced continuously from the printed sheet as the printed sheet travels through the dryer and crosses the multiple air jets. By generating a uniformly spaced series of high velocity air jets, it is possible to scrub and break-up the moisture-laden air layer that adheres to the printed surface of the sheet. The high-velocity air jets create turbulence which overcomes the surface tension of the moisture and separates the moisture laden air from the surface of the paper. The moisture laden air becomes entrained in the forced air flow and can be extracted from the press. In the radiant heat dryer of the present invention, means can be provided for limiting heat transfer to nearby press parts and equipment, and the effective exposure time of a freshly printed sheet to forced air flow can be increased so that the printing press may be operated at high speeds without compromising quality. After a printed sheet exits the dryer, and before the arrival of the next successive printed sheet, residual moisture-laden air can be completely exhausted from the press by an extractor. In such an arrangement, the drying of each printed sheet can be accelerated before it is placed on the delivery stack. If a protective coating is applied over the ink, the coating is completely dried and a dry film is established over the wet ink. This permits the ink to thoroughly cure under the coating after stacking, thus eliminating the need for spray powder to control offsetting defects. Further features and advantages of the present invention will be understood by those skilled in the art upon reading the detailed description which follows with reference to the attached drawings, wherein: FIGURE 1 is a schematic side elevational view in which the dryer of the present invention is installed in a four color offset rotary printing press; FIGURE 2 is a simplified side elevational view showing the installation of the dryer of the present invention in the delivery conveyor section of FIGURE 1; FIGURE 3 is a perspective view, partially broken away, showing installation of the dryer assembly of FIGURE 2 on the gripper chain guide rails; FIGURE 4 is a simplified schematic diagram showing the principal dryer components of the present invention; FIGURE 5 is a sectional view of the improved dryer of the present invention taken along the line 5-5 of FIGURE 4; FIGURE 6 is an elevational view, partially in section, of the dryer assembly shown in FIGURE 2; and, FIGURE 7 is a top plan view, partially in section, of the dryer assembly shown in FIGURE 2. As used herein, the term "processed" refers to various printing processes which may be applied to either side of a sheet or web, including the application of inks and/or coatings. The term "substrate" refers to sheets or web material. "High velocity air" means ambient air which is forced by a blower fan to flow-through a supply conduit. Referring now to FIGURE 1, the dryer 10 of the present invention will be described as used for drying freshly printed substrates, either sheets or web material, which have a protective and/or decorative coating which has been applied in a sheet-fed or web-fed, rotary offset or flexographic printing press. In this instance, the dryer 10 of the present invention is mounted on the guide rails of the delivery conveyor of a four color printing press 12 which is capable of handling individual printed sheets having a width of the approximately 40'' (102 millimeters) and capable of printing 10,000 sheets or more per hour, such as that manufactured by Heidelberg Druckmaschinen AG of Germany under its designation Heidelberg Speedmaster 102V. The press 12 includes a press frame 14 coupled on the right end to a sheet feeder 16 from which sheets, herein designated S, are individually and sequentially fed into the press, and at the opposite end, with a sheet delivery stacker 18 in which the finally printed sheets are collected and stacked. Interposed between the sheet feeder and the sheet delivery stacker 18 are four substantially identical sheet printing units 20A, 20B, 20C and 20D which can print different color inks onto the sheets as they are moved through the press. As illustrated in FIGURE 1, each sheet fed printing unit is of conventional design, each unit including a plate cylinder 22, a blanket cylinder 24 and an impression cylinder 26. Freshly printed sheets from the impression cylinder 26 are transferred to the next printing unit by transfer cylinders T1, T2, T3. A protective coating is applied to the printed sheets by a coating unit 28 which is positioned adjacent to the last printing unit 20. The freshly printed and coated sheets S are transported to the delivery stacker 18 by a delivery conveyor system, generally designated 30. Referring now to FIGURE 1, FIGURE 3 and FIGURE 5, the delivery conveyor 30 is of conventional design and includes a pair of endless delivery gripper chains 32A, 32B shown carrying laterally disposed gripper bars 34 (FIGURE 5) having a gripper element G for gripping the leading edge E of a freshly printed sheet S as it leaves the impression cylinder 26. As the leading edge E of the printed sheet S is gripped by the gripper G, the delivery chains 32A, 32B pull the gripper bar 34 and sheet S away from the impression cylinder and transports the freshly printed and coated sheet to the sheet delivery stacker 18. Prior to delivery to the sheet delivery stacker 18, the freshly printed sheets are dried by a combination of infra-red thermal radiation, forced air flow and extraction. Referring now to FIGURE 2, FIGURE 3, FIGURE 4 and FIGURE 5, the dryer 10 includes as its principal components a dryer head 36, a radiant heat lamp assembly 38, and an extractor head 40. As shown in FIGURE 3 and FIGURE 5, the dryer head 36 is mounted on the upper section 42A of a chain guide rail 42, and likewise on the upper chain guide section 44A of a chain guide rail 44. In the operative position, the dryer head 36 is extended across and spaced from the substrate travel path P (FIGURE 4). The dryer head 36 includes a housing 46 defining an air distribution manifold chamber 48. The air distribution manifold housing includes multiple inlet ports 50A, 50B, 50C and 50D for receiving high velocity ambient air through a supply duct 52 from a blower fan 54. As shown in FIGURE 7, the air distribution manifold housing 46 includes a distribution panel 56 which is intersected by multiple discharge ports 58 which are oriented for discharging jets of heated air toward the sheet travel path. The discharge ports 58 are uniformly spaced so that a uniform blanket of pressurized air is discharged across the processed side of a sheet S as it moves through the dryer. Referring now to FIGURE 6 and FIGURE 7, the heat lamp assembly 38 includes an array of heat lamps 60 extending transversely with respect to the sheet travel path P substantially in parallel relation with each other. The radiant heat lamps 60 are supported between the sheet travel path P and the air distribution manifold by end brackets 62, 64. The ends of each heat lamp project through circular apertures formed in the end brackets. Each heat lamp 60 includes electrodes 60A, 60B which are electrically connected to power buses 66, 68 by flexible, conductive straps 70, 72, respectively. According to this arrangement, each heat lamp 60 is free to expand and contract longitudinally in response to thermal cycling. Each heat lamp 60 is preferably an infra-red radiant lamp having an output in the short wavelength (near) infra-red region (from about 0.70 to about 1.50 micrometers). The power dissipation of each infra-red lamp may be selected from the range of 500 watts - 2 kw. In the exemplary embodiment, each lamp 60 is a short wavelength infra-red quartz lamp having an electrical power rating of 1 kw. Referring now to FIGURE 2, FIGURE 4, FIGURE 5 and FIGURE 6, the extractor head 40 includes identical extractor manifolds 40A, 40B mechanically attached to the lower guide rail section 42B, 44B of the chain guide rails 42, 44, respectively. The extractor head 40 is disposed in an operative position facing a freshly processed sheet as it moves along the sheet travel path P. According to this arrangement, an exposure zone 74 is bounded between the dryer head 36 and the extractor head 40, and is substantially co-extensive with the length and width of the radiant heat lamp assembly 38. Referring to FIGURE 5, each extractor manifold 40A, 40B includes housing panels 41, 43 defining an air extractor manifold chamber 76 on laterally opposite sides of the exposure zone. Each manifold chamber 76 has an inlet port 88 coupled in air flow communication with the exposure zone 74. The extractor head 40 also includes an air circulation passage 78 which is enclosed between a lower manifold panel 80 and a support plate 82. The support plate 82 defines the lower boundary of the exposure zone 74, and limits downward deflection of the trailing end of the sheet S. The support plate 82 is reinforced by multiple ribs 83 which extend between the support plate and the manifold panel 80. The support plate 82 and the ribs 83 serve as a heat sink for conducting thermal energy out of the exposure zone 74, in response to heat exchange with cooling air flowing through the air circulation passage 78. The air circulation passage 78 has an inlet port 84 connecting the air circulation passage in flow communication with a source of cooling air (for example ambient air), and a vent port 86 connecting the air circulation passage 78 in air flow communication with the extractor manifold chamber 76. As shown in FIGURE 4 and FIGURE 5, the extractor manifold inlet port 88 is coupled in air flow communication with the exposure zone 74 for extracting heat and moisture laden air out of the dryer. The extractor manifold chamber 76 is coupled in air flow communication with an exhaust blower fan 90 by an air duct 92. The air flow capacity of the exhaust blower fan 90 is preferably about four times the flow capacity provided by the forced air blower fan 54. This will ensure that the exposure zone 74 is maintained at a pressure level less than atmospheric, thereby preventing the escape of hot, moisture laden air into the press room. Referring now to FIGURE 4, FIGURE 5, and FIGURE 7, a reflector plate 94 is mounted intermediate the air distribution panel 56 and the heat lamp assembly 38. The reflector plate is intersected by multiple air flow apertures 96 which are disposed in air flow communication with the discharge ports 58 which are formed in the distribution panel 56. The air flow apertures 96 are oriented to direct jets 98 of pressurized air through the heat lamp assembly and onto a printed and/or coated (processed) sheet S moving along the sheet travel path. In this illustrated embodiment the multiple air flow apertures are arranged in linear rows 100, 102, 104, 106 and 108 which extend transversely with respect to the direction of sheet travel. The rows are longitudinally spaced with respect to each other along the sheet travel path. Each air jet expands in a conical pattern as it emerges from the air flow aperture 96. Expanding air jets 98 from adjacent rows overlap along the sheet travel path, thereby producing a turbulent air blanket which scrubs the processed side of the sheet S as it moves through the exposure zone. Preferably, balanced air pressure is applied uniformly across the sheet S to ensure that the moist air layer is completely separated and extracted. Referring again to FIGURE 5 and FIGURE 7, the air distribution manifold discharge ports are arranged in similar linear rows which are spaced with respect to each other and are aligned with the rows in the reflector plate. In this arrangement, the discharge ports 58 in each row of the distribution manifold are aligned in flow registration with the air flow apertures 96 in each row of the reflector plate, respectively. Preferably, the air flow apertures 96 in the reflector plate are substantially centered with respect to adjacent heat lamps 60 whereby each pressurized air jet 98 is directed through one of the longitudinal spaces between adjacent lamps (see FIGURE 5). As shown in FIGURE 5, the sheet support plate 82 faces the radiant heat lamps across the exposure zone 74 and is disposed substantially in alignment with the sheet travel path P for engaging the back side of a freshly processed sheet S as it is travels through the exposure zone. The leading edge E of the sheet S is gripped by the gripper means G, and the depending body portion of the sheet S rides on a thin air cushion AC along the support plate 82. Referring again to FIGURE 4 and FIGURE 6, the reflector plate 94 is pre-stressed to assume the form of a convex arch under ambient temperature conditions, and approaches a flat plate configuration under production operating temperature conditions. According to this arrangement, the reflector plate 94 is prevented from touching the infra-red lamps 60 during production. The reflector plate 94 has side edge portions 94A, 94B which are mounted on first and second shoulder brackets 110, 112, respectively, on opposite sides of the dryer head. The shoulder brackets limit thermally induced deflection movement of the reflector plate 94 toward the heat lamps, while accommodating thermally induced lateral expansion and contraction movement of the reflector side edge portions 94A, 94B, respectively.

Claims: A dryer (10) for use on a printing press (12) of the type having conveyor apparatus (30) for transferring a freshly processed substrate (S) along a substrate travel path (P), the dryer including a dryer head (36) adapted for installation in an operative position adjacent a substrate travel path (P), thereby defining an exposure zone (74) therebetween, the dryer head including a housing (46) defining an air distribution manifold having an inlet port (50A, 50B, 50C, 50D) for receiving pressurized air, a reflector plate (94) disposed adjacent the air distribution manifold, the reflector plate being intersected by multiple air flow apertures (96) arranged to direct jets (98) of pressurized air from the air distribution manifold into the exposure zone, and a heat lamp assembly (38) including multiple heat lamps (60) disposed intermediate the reflector plate and the substrate travel path, characterized in that: the multiple air flow apertures (96) are substantially uniformly distributed along the substrate travel path to deliver a substantially uniform blanket of pressurized air across the substrate travel path (P). A dryer (10) as defined in claim 1, wherein the multiple air flow apertures (96) are arranged in a plurality of rows (100, 102, 104, 106, 108) extending transversely to the direction of substrate travel, the apertures being substantially evenly spaced from each other in each row, and the rows being substantially evenly spaced from each other. A dryer (10) as defined in claim 2, wherein the heat lamps (60) are substantially evenly spaced from each other, and the rows of air flow apertures (96) are substantially aligned with the spaces between adjacent heat lamps (60), whereby air jets (98) are directed through the spaces between adjacent heat lamps. A dryer (10) as defined in any one of the claims 1 to 3, wherein an extractor head (40) is disposed adjacent the travel path (P), the extractor head including a housing (40A, 40B) defining an air extractor manifold chamber (76) having an inlet port (88) coupled in airflow communication with the exposure zone (74) for extracting air from the exposure zone and having an air duct (92) for exhausting the extracted air from the press. A dryer (10) as defined in claim 4, wherein the air extractor head (40) comprises a first extractor manifold (40A) having an inlet port (88) coupled in air flow communication with the exposure zone (74) along one side of the travel path (P), and a second extractor manifold (40B) having an inlet port (88) coupled in air flow communication with the exposure zone (74) along the opposite side of the travel path (P). A dryer (10) as defined in any one of the preceding claims, wherein a support plate (82) is disposed adjacent the exposure zone (74) in sheet transfer alignment with the substrate travel path (P) for guiding a freshly processed substrate (S) as it is transferred through the exposure zone, and a cooling air circulation manifold has a housing panel (80) spaced from the substrate support plate (82) defining an air circulation passage (78) therebetween, the air circulation manifold having an inlet port (84) for connecting the air circulation passage in communication with a source of pressurized cooling air, and having a vent port (86) for exhausting cooling air from the air circulation passage. A dryer (10) as defined in any one of the preceding claims, wherein the reflector plate (94) is prestressed to assume the form of a, convex arch under ambient temperature conditions. A dryer (10) as defined in any one of the preceding claims, wherein first and second support shoulders (110, 112) are formed on opposite sides of the dryer head (36), the reflector plate (94) having first and second side edge portions (94A, 94B) engagable with the first and second support shoulders, respectively, the support shoulders being arranged to limit thermally induced deflection movement of the first and second side edge portions toward the heat lamp assembly.

Inventors: COPENHAVER PAUL DRAKE, RENDLEMAN RONALD MEROD, SECOR HOWARD CURTIS, COPENHAVER, PAUL DRAKE, RENDLEMAN, RONALD MEROD, SECOR, HOWARD CURTIS
Applicants: DEMOORE HOWARD W, DEMOORE, HOWARD W.
Application year: 1994
Main classification: B41F23
IPC codes: F26B13, B41F23, F26B3